The present invention relates to a pressure control device to be inserted into a connection between a wheel brake at the front axle and at least one wheel brake at the rear axle of an automotive vehicle, which device sets a hydraulic pressure in the wheel brake of the rear axle in dependence upon the pressure in the wheel brake of the front axle, wherein two valve pistons which are connected in parallel in respect of effect are arranged in cylinder bores displaceable by the pressure of the wheel brake of the front axle in opposition to a control force, wherein, after a proportional pressure rise in the wheel brakes upon attainment of a definable change-over pressure a pressure will be set in the wheel brake of the rear axle which is reduced in relation to the pressure in the wheel brake of the front axle.
A device incorporating the preceding features is known from U.S. Pat. No. 3,359,729. This known device comprises two valve pistons guided in cylinder bores, with each of said valve pistons being acted upon by the pressure of a master cylinder. These valve pistons are axially slidably guided in cylinder bores in a sealed relationship therewith and are loaded by compression springs which counteract the forces of the master cylinder pressure. Arranged at one of the valve pistons is a sealing member which moves into abutment on a valve seat in the presence of a predeterminable master cylinder pressure and interrupts one of the two connections between the master cylinder and the wheel brake to be controlled. After closure of this hydraulic connection, exclusively the other valve piston will now remain effective upon a further pressure increment in the master cylinder, the said valve piston projecting with an end face seal-tightly into an inlet chamber which is hydraulically connected to the master cylinder. The end face of this valve piston that is remote from the inlet chamber projects into an outlet chamber which latter forms a closed hydraulic system in conjunction with the wheel brake to be controlled. Therefore, upon a further pressure increase in the master cylinder, the valve piston will be displaced into the outlet chamber in opposition to the force of a compression spring, while there is decrease of the volume of the portion of the brake system that is connected to the wheel brake, so that a pressure rise takes place in the wheel brake which is first of all determined by the spring rate of the compression spring supporting the valve piston and which is reduced in a predetermined ratio relative to the master cylinder pressure.
It has to be regarded as a disadvantage in the pressure control device described that it is in total of relatively intricate design and that the valve seat at the one valve piston necessitates a rubber seal which is subject to natural wear.
It is therefore an object of the present invention to provide a straightforwardly designed pressure control device of the species initially referred to, wherein structurally largely identical components are used and wherein the function desired will be accomplished also in the absence of rubber-elastic sealing means.